Characterization of Distinct Stat5b Binding Sites That Mediate Growth Hormone-stimulated IGF-I Gene Transcription

• Published in: The Journal of biological chemistry 2006-02, Vol.281 (6), p.3190-3197
• Main Authors: Chia, Dennis J., Ono, Mitsuru, Woelfle, Joachim, Schlesinger-Massart, Mylynda, Jiang, Honglin, Rotwein, Peter
• Format: Article
• Language: English
• Subjects: Animals; Binding Sites; Binding, Competitive; Chlorocebus aethiops; Chromatin Immunoprecipitation; COS Cells; DNA - chemistry; DNA Primers - chemistry; DNA, Complementary - metabolism; Exons; Genes, Reporter; Growth Hormone - metabolism; Insulin-Like Growth Factor I - metabolism; Male; Models, Genetic; Plasmids - metabolism; Promoter Regions, Genetic; Protein Binding; Rats; Rats, Sprague-Dawley; Recombinant Proteins - chemistry; Response Elements; Reverse Transcriptase Polymerase Chain Reaction; RNA - metabolism; STAT5 Transcription Factor - chemistry; STAT5 Transcription Factor - metabolism; Transcription, Genetic; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M510204200

A key agent in the anabolic actions of growth hormone (GH) is insulin-like growth factor-I (IGF-I), a 70-amino acid secreted protein with direct effects on somatic growth and tissue maintenance and repair. GH rapidly and potently stimulates IGF-I gene transcription by mechanisms independent of new protein synthesis, and recent studies have linked the transcription factor Stat5b to a regulatory network connecting the activated GH receptor on the cell membrane to the IGF-I gene in the nucleus. Here we analyze two distinct conserved GH response elements in the rat IGF-I locus that contain paired Stat5b sites. Each response element binds Stat5b in vivo in a GH-dependent way, as assessed by chromatin immunoprecipitation assays, and consists of one high affinity and one lower affinity Stat5b site, as determined by both qualitative and quantitative protein-DNA binding studies. In biochemical reconstitution experiments, both response elements are able to mediate GH-stimulated and Stat5b-dependent transcription when fused to a reporter gene containing either the major IGF-I promoter or a minimal neutral promoter, although the paired Stat5b sites located in the second IGF-I intron were more than twice as effective as the response element that mapped ∼73 kb 5′ to the IGF-I exon 1. Taken together, our results define the initial molecular architecture of a complicated GH-regulated transcriptional pathway, and suggest that apparently redundant hormone response elements provide a mechanism for amplifying GH action at a physiologically important target gene.